1. Field of the Disclosure
The present subject matter is generally directed to performing drilling activities with mobile drilling rig assemblies, and in particular, to systems and methods that may be used to perform simultaneous operations on multiple wellbore locations with a single mobile drilling rig.
2. Description of the Related Art
In some land-based oil and gas drilling applications, the drilling operations that are performed at a given oilfield drilling site may involve drilling a plurality of relatively closely spaced wellbores, sometimes referred to as “pad” drilling operations. In pad drilling, the distance between adjacent wellbores may be as little as approximately 5-6 meters (16-20 feet) or even less, and the wellbores are oftentimes arranged in a two-dimensional grid pattern, such that rows and columns of wellbores are disposed along lines that run substantially parallel to an x-axis and a y-axis, respectively.
In such pad drilling applications, in order to maintain efficiency and overall cost-effectiveness of the drilling operations, it is necessary to move the drilling rig between such closely spaced adjacent wellbores after drilling operations have been completed at one wellbore. Accordingly, mobile—or even self-moving—drilling rigs are oftentimes employed in pad drilling operations, which thereby avoids the costly and time-consuming use of a crane for disassembling, lifting, and moving the various drilling rig components to the next wellbore location before drilling operations can recommence. The use of mobile drilling rigs helps to avoid a certain amount of “flat time” during the overall pad drilling operations, that is, the down time during which actual drilling wellbore drilling is not taking place, thereby more efficiently utilizing the time and capabilities of highly expensive drilling rigs.
However, it should be appreciated that, irrespective of the greater overall efficiency that mobile drilling rigs may bring to pad drilling applications, there is still a great amount of flat time associated with the conventional wellbore drilling activities associated with a given wellbore. Such additional flat time often occurs when ancillary wellbore operations other than the actual drilling—i.e., the time during which a drill string and drill bit are used to actually advance the wellbore into the earth—are performed when a drilling rig is in position above the wellbore. For example, the drilling rig cannot drill when the wellbore is being prepared for the drilling phase, such as by positioning a blowout preventer (BOP) on a wellhead and performing testing operations in order to ensure that wellbore drilling can be performed in a substantially safe fashion. Additionally, once a given section of the wellbore has been drilled to a desired depth, completion operations, including casing and cementing operations, must be performed to line the borehole so as to provide additional support and a pressure-tight seal.
During the casing operation, casing must be run into and set in the wellbore. Typically, the casing serves several purposes, including, among other things, preventing the drilled borehole from collapsing, providing a means of containing formation pressures, confining production to the wellbore, preventing inter-formational flow, and/or to permitting production from a specific zone. Thereafter, a cementing operation must be performed in order to provide support for and “bond” (i.e., attach) the casing to the formation, to protect the producing formations, to help in the control of blowouts from high-pressure zones, and/or to form a seal in the event of a “kick” during further drilling operations.
During the wellbore preparation phase described above, the drilling rig is essentially standing idle above the wellbore, other than to perhaps facilitate the lifting and placing of the BOP onto the wellhead. Additionally, while the drilling rig is actively working during the casing phase of completion operations, that is, when the casing is being run into the borehole, the drilling rig is again standing substantially idle above the wellbore during cementing operations, as drilling operations on subsequent deeper wellbore sections cannot commence until the cement has been pumped into place, and sufficient time has passed to allow the cement to set up. The additional flat time associated with the wellbore preparation and completion phases of the overall drilling program may thus have a significant impact on overall drilling costs at a given pad drilling site.
Accordingly, there is a need to develop and implement new designs and methods that maximize, or at least increase, the efficiency mobile drilling rigs when drilling closely-spaced adjacent wellbores during pad drilling operations. The following disclosure is directed to mobile drilling rig systems and methods that may be used to address, or at least mitigate, at least some of the problems outlined above.